Continuous electrical logging



Feb. l, 1955 J. J. ARPS 2,700,897

CONTINUOUS ELECTRICAL LOGGI'NG' Filed Sept. 2C, 1950 2 Sheets-Sheet lFf/Mj.

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gil/n Feb. l, 1955 J. J. ARPS CONTINUOUS ELECTRICAL LOGGING 2Sheets-Shee?l 2 Filed Sept. 20, 1950 INVENTOR JAW Jaco 142/25,

ATTORNEY United States Patent Office 2,700,897 Patented Feb. 1, 1955CONTINUOUS ELECTRICAL LOGGING Jan J. Alps, Tulsa, Okla.

Application September 20, 1950, Serial No. 185,849

8 Claims. (Cl. 715-152) This invention relates in general to electricalexploration of the geological strata traversed by earth boreholes andmore particularly to methods and apparatus for the lslinliultaneouselectrical logging and drilling of well boreo es.

In the conventional methods of electrical logging of earth boreholes asheretofore usually practiced, a source of electric current has beenlocated at the surface of the earth outside of the borehole and acurrent therefrom has been applied, through an insulated cable loweredinto the borehole, to a portion of the penetrated geological strata tobe explored, and the results of such exploration transmitted back up theborehole to the earth surface through the same or separate insulatedconductors in the cable. The provision of insulated conductors in adrilling well together with the drill pipe in such manner that drillingand electrical logging operations can be carried on simultaneously, hasbeen found to be of doubtful practicability. Therefore, the usualpractice has been to interrupt the drilling operation at intervals topermit the removal of the drill pipe from the borehole and the runningof the logging apparatus suspended from a conductor cable in theborehole in the absence of the drill pipe.

This has the disadvantage that the precise control of the depth ofdrilling with respect to certain formations is difficult, with theresult that in many cases the desired shale body or the possibleproductive formation may have been drilled through or passed up,possibly necessitating subsequent time consuming and expensivecorrective measures before the next intended steps in the process ofcontinued drilling or completion of the well can be undertaken.

Another disadvantage in the before described usual method of electricallogging resides in the well known fact that the liquid from the drillingfluid invades the penetrated formations surrounding the borehole,thereby changing the electrical characteristics of such formations for asubstantial distance laterally from the borehole axis. Such invasion isprogressive with time and if permitted to continue for an appreciablelength of time, results in sufficient contamination of the formations tocause possible confusion in the correct interpretation of the electricalcharacteristics of the formations thus measured.

The before described difficulties are largely overcome by the presentinvention which does not require insulated conductors in the borehole atany time but provides for the transfer of the results of the electricallogging operations or other similar operations within the borehole tothe earth surface without employing the usual interconnecting insulatedconductors, and this can be accomplished while the drill pipe is in thewell borehole and during drilling operations. The system of the presentinvention furthermore permits the electrical logging apparatus to beembodied in or contained within the drilling tools, and the process ofelectrical logging to be carried on simultaneously with the drilling ofthe borehole whereby the electrical logging measurements can be made ofthe freshly penetrated formations before excessive invasion of drillingfluid into the formation takes place.

Another advantage of the present invention resides in the substantiallysimultaneous drilling and logging of a formation which it provides,thereby permitting a continuous and more accurate determination of thedepth of the borehole relative to the formations penetrated thereby,than is possible by the intermittent, alternate drilling and loggingoperations heretofore usually employed. In other words, by employment ofthe method and apparatus of the present invention an electrical log maybe made and observed while drilling operations are in progress and thedrilling operations modified as desired or stopped immediately at thetime the electrical log being recorded indicates the desirability ofsuch modication or stoppage.

Accordingly, an object of this invention is to provide a method andapparatus for electrical logging of geological strata traversed by aborehole in which the necessity of using an insulated conductorextending into the borehole to the logging apparatus within the boreholeis avoided.

Another object of this invention is to provide an electrical loggingsystem which permits the conducting of electrical logging operations anddrilling operations simultaneously.

Another object of this invention is to provide a system for transmittinginformation from a point within a well borehole to a point outside ofthe borehole during drill- 'ng1 and while the drilling tools are presentin the bore- The objects of this invention are attained, in brief, byutilizing the circulating drilling uid to carry hydrogen tracer gas tothe top of the borehole. This hydrogen tracer gas is generated byelectrolysis of the liquid portion of the drilling fluid at theexploring electrode, by the action of and in proportion to the exploringcurrent which flows between such electrode and the adjacent surroundingborehole formations. Upon arrival of the thus generated hydrogen at thetop of the borehole as conveyed in the circulating drilling fluid, it isseparated and measured by means of a suitable hydrogen gas detector.Measurements thus obtained provide indirect continuous measurements ofthe exploring electrode current and therefore are indicative of theconductivity or resistivity gf 1the formations opposite the electrodewithin the bore- Other objects, advantages and features of novelty willbe evident hereinafter in the more detailed description of theinvention.

In the drawings which illustrate a preferred embodiment and mode ofoperation of the invention and in which like reference charactersdesignate the same or similar parts throughout the several views:

Figure l illustrates the general arrangement of the apparatus of theinvention as applied to a drilling well borehole.

Figure 2 illustrates alternative apparatus to be employed in connectionwith the apparatus of Figure l.

Figure 3 illustrates a modified form of the apparatus of Figure 1.

The apparatus is as follows:

Referring primarily to Figure l, a longitudinal section of a typicalwell borehole is shown, by way of example, having a lower uncasedportion 10 and an upper portion in which a surface string of casing 11has been set. Within the borehole is shown conventional rotary drillingapparatus comprising a drill bit 12, a drill collar 13 and a drill stemor drill pipe 14 connected at its upper end through a square kelly 15 toa swivel 16, which is in turn supported by a hook 17 suspended from asuitable drilling line traveling block 123 and from well dei-rickapparatus thereabove (not shown). The square kelly 15 passes throughconventional gripping means in a rotary table 20 which is adapted to berotated by means of the usual beveled gear and pinion drive illustratedat 21 and 22 respectively. The pinion 22 is arranged to be driven, inaccordance with usual practice, through shaft 23 by a suitable primemover.

The circulation passage through the drill stern and swivel 16 isconnected through flexible hose coupling 25 and piping 26 to a suitabledrilling fluid circulating pump 27, the suction of which is taken,through suction inlet pipe 28, from a mud settling pit 29. The upper endof the surface casing 11 which provides a return path for circulatingdrilling fluid from the borehole, is provided with a lateral outlet pipe31 which extends into the upper end portion of a closed separatorchamber 32. The said lateral pipe 31 is provided inside of the separatorchamber with a downwardly curved elbow 33. Below the elbow 33 and withinthe separating chamber 32 are provided a plurality of oppositelypositioned, inwardly sloping bafties 35. The lower end of the separatingchamber 32 is provided with a conical bottom 36 which leads into anoutlet pipe 37 which in turn extends downwardly and laterally into atrough 39 leading to the top of the settling pit 29. C

The separator chamber 32 is connected to suitable hydrogen detecting andmeasuring apparatus as hereinafter described. Chamber 32 is connected atthe top end by way of pipe 40 and through a valve 42 to a cham ber 43,containing an electrically conductive heater fila ment 44, and thencethrough connecting piping to the inlet 46 of a suitable exhaust fan orblower 47 having a discharge or outlet connection 48. Thebeforementioned inlet 46 of the blower 47 is also connected throughanother branch pipe connection 49 to a chamber 50, similar to chamber43, containing an electrically conducting heater filament 51 similar tofilament 44, and thence the connection extends through connection 52 andvalve 53 into a lower portion of the separator charnber 32 at 54.

The electrically conducting heater lament 44 is supported within chamber43 by means of conductors 55 and 56 which pass through suitable sealedlead-in insulators 57 and 58 in the walls thereof, and the electricallyconducting heating filament 51 is similarly supported within chamber Si)by means of conductors 60 and 61 3 which pass through sealed lead-ininsulators 73 and 74. Conductors and 61 leading from the filaments 44and 51, respectively, make common connection at 62, and conductors 56and 60 leading from the opposite ends of the filaments make connectionwith substantially identical resistors 64 and 65 which in turn areconnected through conductors 66 and 67, respectively, to opposite endsof resistor 68. A conventional voltmeter or galvanometer V is connectedbetween connection 62 and a contactor 69 which makes sliding contactwith the resistor 68. The circuit thus formed is, in effect, that of aconventional Wheatstone bridge arrangement, Current is supplied to thebridge circuit, from a suitable battery 69, through conductors 70, 71and a variable resistor 72. Voltmeters 75 and 76 may be connected acrossthe filaments 44 and 51, respectively. Filaments 44 and 51 arepreferably made of a material which has a high temperature coefficientso that small changes in temperature will cause comparatively largechanges in the electrical resistance thereof. Suitable materials forthese filaments are preferably those not subject to oxidation and maybe, for example, a noble metal such as platinum, gold, nickel or alloysthereof.

Referring now to the lower end of the drill stem, the drill collar 13 isprovided with an outside insulating covering 77 which may be composed ofan inner instilating sleeve or tubing member 78 fitting snugly over thefull length of the drill collar from the top of the drill bit 12 to theupper end of the drill collar. A pair of spacedapart electrode rings 81and 32 are carried by the insu- )ating sleeve 78 and are insulated fromthe drill collar 13 thereby, said electrodes being normally exposed tocontact with surrounding drilling fluid. These electrode rings may bemade of platinum or a similar noble metal. The insulating sleeve 78 iscovered above, below and between the electrode rings 81 and 82 by aplurality of protective insulating ring members placed end-to-end asshown at 79. Such rings are preferably made of rubber or the likematerial and are of such thickness as to protect the recessed electrodesS1 and S2 and the insulating sleeve 79 from abrasion by the boreholewalls. Conventional casing protector rings may be here employed. Thedrill collar 13 is provided on its interior with a suitable fluid tightcontainer or cavity schematically designated at 83 for containing abattery 84 and switching apparatus as hereinarter described.

The battery 84 has its positive terminal connected through conductor 55,fluid circulation pressure operated switch 86 and conductor S7 with abrush 88. The negative terminal of the battery S4 is connected throughconductor S9 with a brush 90. Brushes 38 and 90 are positioned to makeelectrical contact at diametrally opposite points with a reversingcommutator 91 having a pair of opposite, conductive commutator segments92 and 93 insulated from one another and each of which extend aroundslightly less than half the circumference of the insulating commutatordisc 94. A pair of diametrally opposite brushes 95 and 96 are positionedto make contact with the commutator 91 at right angles to the diametralline of Contact of brushes 88 and 90, said brushes 95 and 96 beingconnected through Conductor 100 and 101 respectively with thebeforementioned ring electrodesl 81 and 82.

The commutator 91 is coupled for rotation, through a shaft 103 to amotor 104. The motor 104 is adapted to be supplied with current frombattery 84 through conductors 105 and 106 from conductors 89 and S7respectively When switch 107 is closed. The iiuid circulation pressureoperated switch 86 may be constructed in a manner similar to thatdisclosed in copcnding Arps application, Serial No. 68,930, now PatentNo. 2,658,284.

Referring now primarily to Figure 2, recording apparatus is thereillustrated employing a voltmeter or galvanometer V1 which may be thesame or similar to the galvanometer or voltmeter shown at V in Figure l,the conductors 62 and 69 being adapted to make connection at junctionpoint 62 and movable contact 69 respectively, in the hydrogen detectionand measuring apparatus of Figure l. The hand 110 of the voltmeter orgalvanometer V1 carries at its outer end a pen which bears upon a chartor strip of graph paper 111 adapted to be moved between rollers 112 and113 for the purpose of tracing a curve or making a graph as illustratedat 115. The chart 111 may be driven by a suitable motor 116 coupledthrough shaft 117 to one of the rollers such as the roller 113. The rateof drive of the roller 113 may be such that the chart 111 is moved at agiven constant rate with respect to time or preferably at a rate orhaving a motion proportional to the longitudinal motion of the drillstem 13 and accompanying electrodes 81, 82, into or out of the wellborehole. This proportional motion may be accomplished by varioussuitable means such as, for example, employing a line 120 passing overpulleys 121 and 122 and extending between the traveling block 123 and adrum 124, said drum being coupled to a Selsyn generator 12E: and theSelsyn generator in turn being coupled through suitable electricalconnections, as shown at u, b and c, to a Selsyn motor at 116. Anotherapparatus suitable for this purpose is illustrated in Figure 2 ofcopending Arps applications Serial No. 619,629, filed October l, 1945,now Patent No. 2,524,031, and Serial No. 269,568, tiled Feb. l, 1952.

Referring now primarily to Figure 3, radioactivity of the formations maybe measured by the apparatus modification there shown. A radioactivityradiation detector which may be of any conventional type such as theGeiger counter, ionization chamber or the like devices responsive togamma rays, neutrons or the like radiations is connected through battery131 across resistor 132. Resistor 132 is in turn connected throughconducotrs 133 and 134 across the input terminals of a suitableamplilier means A. One terminal of the output of the amplifier means Ais connected through conductor 135 to the battery 84 and thence throughconductor 85. switch 86 and conductor 87 to the brush 38 of thecommutator 91. The other output terminal of means A is connected throughresistor 136 and conductor 137 to brush 90 of the commutator 91. Theamplifier device A may be of conventional design and such that thecurrent fiow from battery through the output thereof bears apredetermined functional relationship to the input signal appearingacross resistor 132, which in turn is representative of the radiationintercepted by the detector 130.

The operation of the apparatus is as follows:

ln operation of the drilling apparatus of a drilling well, the drillingfluid which is usually an aqueous sus-A pension of clayey materials, iswithdrawn from the pit 29 through the suction pipe 28 and forced bymeans of pump 27 through pipe 26 and coupling 25 into the top of theswivel 16 and thence down through the interior of the kelly 15, drillpipe 14, drill collar 13 and out through suitable discharge holes, asillustrated at S9, in the drill bit 12. The circulating drilling 'fluidthen News upwardly in the annular space formed between the borcholewalls and the drill stem as indicated by arrow :33, and up through thesurface casing 11, from the top of which it is finally dischargedthrough the lateral discharge pipe 31 into the top of the separator 32.in the separator 32 the drilling uid passes or falls downward over thebaie plates 35 to the bottom of the chamber from where it is finallydischarged through pipe 37 into the trough 39 from which it fiows intothe top of the settling pit 29 to complete the cycle of circulation.

Meanwhile, during circulation of the drilling fluid as hereinbeforedescribed, the drill stem comprising the kelly 15, drill pipe 14, drillcollar 13 and drill bit 12, may be rotated by means of the rotary table20 which is driven by the bevel gear and pinion 21 and 22 respectively,the pinion 22 being driven through the shaft 23 as beforementioned.Drilling operations in the borehole may thus be maintained.

During drilling operations or any other operations, when the drillcollar 13 is maintained in electrical contact with the drilling fiuidWithin the borehole, and under conditions where the drilling fluid isbeing circulated, the fluid operated switch 86 is operated to close thecircuit between conductors 85 and 87. A closed circuit is thereby formedacross the battery 84 permitting a continuous flow of current from thenegative terminal of the battery 84 through conductor 89, brush 90,commutator segment 93, brush 96 and conductor 101, to electrode 82 andthence through the drilling fluid and through a portion of the adjacentformation and return through the drilling fluid to the electrode 81,conductor 100, brush 95, commutator segment 92, brush 88, conductor 87,fluid operated switch 86 and conductor 85, to the positive terminal ofthe battery 84. Since a portion of the formation surrounding theborehole adjacent the electrodes 81 and 82 forms a part of theelectrical circuit across the battery 84, as before described, thecurrent flowing in this circuit will consequently be directlyproportional to or at least representative of the formationconductivity.

The passage of the direct current between the electrodes 81 and 82 whileimmersed in the aqueous drilling fiuid will cause hydrogen gas to begenerated by electrolysis and liberated at the cathode electrode 81. Atthe same time oxygen gas will be generated by electrolysis and liberatedat the anode electrode 82. As is well known two volumes of hydrogen willbe liberated at the electrode 81 for each volume of oxygen liberated atthe electrode S2. The amount of hydrogen gas which will be released atthe cathode 81, per unit of time will be, in accordance with FaradaysLaw, proportional to the current passing between electrodes 81 and 82,and consequently the amount of hydrogen released at electrode 81 will berepresentative or indicative of the conductivity of the adjacentformation.

The conductivity of the drilling fluid in the vicinity of the electrodesS1 and 82 will of course also affect the total conductivity of thecircuit across the battery 84 to some extent but as is well known inthis art, the effect of this conductivity is usually a substantiallyconstant factor and its effect is relatively small as compared to theconductivity of the relatively large volume of surrounding formations.Actually the conductivity of the drilling fluid is often less than thatof the surrounding formations. in any event, the effect of theconductivity of the drilling fiuid is substantially constant and can becorrected for. While the commutator 91 has been shown and hereinbeforedescribed as positioned to connect the positive and negative terminalsof the battery respectively to the electrodes 81 and 82 the commutatormay obviously be positioned, by rotation 90 from the position shown toreverse these polarities, without affecting the mode of operation of theapparatus.

In some cases it may be desirable to apply an intermittently orperiodically reversed current to the electrodes 81 and 82 in order toavoid polarization effects or the deposition of colloids upon thepositive electrode. In such cases the switch 107 is closed manuallyprior to lowering the drill string into the borehole or by othersuitable means after lowering the drill string into the borehole.Closing of the switch 107 energizes motor 104 which in turn drives thecommutator 91 through the coupling shaft 103. Rotation of the commutator91 results in periodic switching and reversal of the polarity of thepotential applied from the battery 84 to the electrodes 81 and 82. Therate of rotation of the commutator and hence the frequency of reversalof the current or voltage applied to the electrodes 81 and 82 should besufficiently low to permit the desired electrolysis and Suitablefrequencies for this purpose may be of the order of 0.1 to 10 cycles persecond. The potential applied to the electrodes by the battery may befrom a few volts above the polarization potential of 1.2 to 1.7 volts,to as high as 100 volts depending upon the current density used, thegeometry and arrangement of electrodes, type of drilling fluid employedand other conditions.

The hydrogen gas which is liberated at electrodes 81 or 82 in the caseof the use of D.C. or at electrodes 81 and 82 in the case of the use ofintermittently or periodically reversed polarity, such liberation beingin quantities representative of the conductivity of the adjacentformation as before described, is conveyed in the circulating drillingmud to the top of the well bore and up through the annular space in thesurface casing 11 in the direction indicated by arrow 102 from where itpasses through the lateral outlet pipe 31 and into the top of theseparator chamber 32. The drilling fluid containing the hydrogen gas isdirected downwardly through the separator chamber 32 by the elbow 33from which it falls down through the chamber over the bafe plate 3S incounter-current contact with upwardly owing air, and finally thedrilling fluid from which hydrogen has been removed, is discharged fromthe bottom of the separator chamber through pipe 37 into the trough 39through which it ows in return to the settling pit 29.

The air which passes upward in counter-current contact with thedownwardly flowing drilling fluid within the separating chamber 32 asbefore described, enters at the bottom through pipe 37 which is onlypartially filled with the outwardly flowing drilling fluid as indicatedby the arrow 34 and passes out of the top of the separating chamber,together with separated hydrogen through pipe 40 and valve 42 and thencethe air-hydrogen mixture flows through the chamber 43 and in contactwith the heater filament 44. The air, after passing through the chamber43 and in contact with the filament 44, flows on through pipe 45 to theinlet 46 of the blower 47 and is finally exhausted from the bloweroutlet 48. At the same time a substantially equal amount ofsubstantially hydrogen-free air is drawn into pipe 52 at a point 54 froma lower portion of the separating chamber, and flows through the chamber50 into contact with the heater filament 51 and thence through pipe 49to the inlet 46 of the blower 47 and is exhausted therefrom at 48together with the air from the other branch pipe 45. By withdrawing airboth from the top and from a lower portion of the separating chamber 32as before described, the air streams passing in contact with thefilaments 44 and 51 will thereby have nearly the same temperatures andhumidities. These quantities of air may be equalized or otherwiseadjusted as desired by means of the valves 42 and 53.

The Whealstone bridge measuring circuit is initially adjusted bymovement of the position of the contact 69 upon the resistor 68 to acondition of balance under which the voltmeter V is zeroed. The currentflowing through the heater filaments 44 and 51 are then adjusted bymeans of the variable resistor 72 such that these filaments are heatedto a temperature below the point where any hydrogen mixture or any otherof the conibustible gases passing over them will ignite. Thisternperature can be carefully controlled, as before stated, by adjustingthe variable resistor 72 and checking with the voltmeters 75 and 76. Thevoltage applied will depend largely upon the total resistance of theheater filaments.

As before explained, filaments 44 and 51 are preferably made of aconductive material which has as high a temperature coefficient aspossible so that a small difference in temperature between the filamentswill cause a comparatively large difference in their electricalresistances, resulting thereby in a comparatively large unbalance of themeasuring circuit which will be reflected in the meter V.

The thermal conductivities, expressed in calories per second per squarecentimeter per degree centigrade per centimeter, of the gases mostlikely to be encountered in the drilling fluid arc as follows:

Air 56.8 10*G Carbon dioxide 30.7X 106 Hydrogen, 0 C 327.0X10-6liberation of hydrogen at each electrode to take place. Hydrogen, 100 C369.0X10-6 arnese? Methane Nitrogen Oxygen (Handbook of Chemistry andPhysics, 23rd edition, page 1456.)

Since, as is apparent from the foregoing table of thermal conductivitiesof various gases, the thermal conductivity of hydrogen gas is relativelyhigh as compared to air, oxygen or any other gases normally found indrilling mud and which may be liberated in the separating chamber 32,the presence of hydrogen in the air from the drilling huid and whichpasses through the chamber 43 will result in withdrawal of a greateramount of heat from tilament 44 than the relatively hydrogen-free airpassing through chamber withdraws from iilament 51, thereby causing agreater cooling or reduction in the temperature of filament 44 than thatof filament 51. The resistance of the filament 44 will thus undergo agreater reduction than that of filament with the result that the bridgemeasuring circuit will be unbalanced in such a way as to retlect thatunbalance in the voltmeter V. The amount of unbalance thus indicated bythe voltmetcr V will, therefore, be indicative or representative of thehydrogen content or" the gas stream owing from the gas separator 32.

By plotting the concentration of hydrogen gas measured in the beforedescribed manner. against or in correlation with the depth of theborehole, by means of the apparatus illustrated in Figure 2, a log asillustrated at 115 will be obtained representing the formationconductivily versus depth. ln such measurements suitable precautions canbe taken to correct for the distance between the bottom of the drill bitand the eliective position of electrodes 81 and 82. Also it may benecessary or dcsirable to adjust the drive mechanism moving the chart111 to compensate for the time necessary for a given volume of thedrilling uid to travel from a point in the borehole opposite theelectrodes 81, 82 to the top ot' the well and through the gas separationchamber 32. Typical means for so adjusting the chart drive mechanism isdisclosed in the applicants copending application Serial No. 269,568,tiled February l, 1952.

instead of employing two separate electrodes as shown at 81 and 82 inFigure 1 the bit itself may be used as one of the electrodes and in suchcase the structure of the drill collar. electrode and electrode bit may,for example, be made as shown in the article by David G. Hawthorn and.lohn E. Owen in the January i940 issue of the Petroleum Engineer, page7l.

The principles of this invention can also, as hei-einbet'ore described,be applied to other measurements such us natural potential, drillingweight on the bit. bottom hole temperature or pressure or radioactivityofthe formation, it being only necessary in order to accomplish this toregulate the ilow of current from the battery 84 to the electrodes 81and 82 and therebetween through the drilling tiuitl in accordance withthe beforcmentioned characteristics to be measured.

For example, the measurement of radioactivity within the well boreholecan be accomplished by the hereinbetorc described apparatus of Figure 3.The operation of this portion of the apparatus is as follows:Radioactivity radiation intercepted by the detector 130 results in apotential drop or in rapid potential pulsations across resistor 132which are applied through conductors 133 and 134 to the input ofampliiier device A. ln the output circuit ot' amplifier device A,current, which is a predetermined function ot` the radiation received bydetector 130, tiows from battery 84 through conductors 85 and .135 tothe one output terminal of the device and thence through resistor 136.conductor 137, brush 99 (and with commutator positioned as shown), brush96 and conductor 101 to electrode 82. From electrode 82 the currentflows through the tluid in the borehole to electrode 8l and returnsthrough conductor 100, brush 92. brush 88, conductor 87, switch 86 andconductor 85 and returns to battery 84. Resistor 136 is made relatively'high so that differences in resistances of the current path betweenelectrodes 82 and Si through the borehole fluid and surroundingformations will have an inappreciable effect upon such current ilow.When commutator 91 is turned 90 from the position shown, the currentflow insofar as electrodes 81 and 82 are concerned will be reversed fromthat just' described.

The hydrogen gas liberated at electrodes 81 and 82 in proportion to thecurrent thus caused to ow therebetween in the operation of the apparatusof Figure 3 is carried in the drilling fluid to the top of the wellwhere it is separated and measured as hereinbefore described inconnection with the apparatus of Figure l.

The terms measuring the quantity of hydrogen as cmployed herein in thespecification and claims are not to be limited in meaning to actualquantitative determination of such values but are to include theactuation of any indicator or recorder means or device such as thevoltmeter or galvanometcr V or V1 or the like device whereby a visualindication or graphical record ot a measure of such values or anindication or graphical record of a value which is indicative of orrepresentative ot` the amount of hydrogen present in the separated gasesor present in the drilling fluid may be obtained.

lt is to be understood that the foregoing is illustrative only and thatthe invention is not limited thereby but may include variousmodifications and changes made by those skilled in the art withoutdistinguishing from the spirit and scope of the invention as defined inthe appended claims.

What is claimed is:

l. A method of logging a well borehole comprising: applying a potentialdifference between a pair of spaced electrodes, vertically shil'tablewithin said borehole and in electrical contact with aqueous tluidtherein whereby hydrogen is generated in said I'luid at said electrodesby electrolysis in quantities which are representative of theconductivitics of the formations surrounding said borchole adjacent saidelectrodes; circulating said fluid containing said hydrogen to the topof the well borehole and there separating hydrogen gas therefrom; andmeasuring the quantity of the separated gas relative to time.

2. A method for logging a well borehole comprising: applying a D.C.potential difference between a pair of spaced electrodes, verticallyshiftable within said borehole and in electrical contact with aqueoustiuid therein whereby hydrogeu is generated in said luid at one of saidelectrodes by electrolysis in quantities which are representative of theconductivity of the formation surrounding said borehole adjacent saidelectrodes; circulating said iluid containing said hydrogen to the topof the well borehole and there separating hydrogen gas therefrom: andmeasuring the quantity of the separated gas relative to time.

3. A method for logging a well borehole comprising: applying a D.C.potential difference between a pair of longitudinally spaced electrodes,vertically shiftable within said borehole and in electrical contact withaqueous tiuid therein whereby hydrogen is generated in said fluid at oneof said electrodes by electrolysis in quantities which arerepresentative of the conductivity of at least a portion of theformation surrounding said bore hole adjacent said electrodes;circulating said tluid containing said hydrogen to the top of thc wellborehole and there separating hydrogen gas therefrom; continuouslymeasuring the quantity of the thus separated gas relative to time; andcorrelating the resultant measurements with the well borehole depth.

4. The method according to claim 3 including the step of periodicallyreversing the polarity of the potential applied to the electrodes.

5. A method for logging a well borehole comprising: applying a D.C.potential diierence between a pair of longitudinally spaced electrodes.vertically shiftable within said bore hole and in electrical contactwith aqueous iluid therein whereby hydrogen is generated in said tluidat one of said electrodes by electrolysis in quantities which arerepresentative of the conductivities of at least a portion of theformations surrounding said borehole adiacent said electrodes;circulating said fluid containing said hydrogen to the top ot the wellborehole and there separatA ing hydrogen gas therefrom; continuouslymeasuring the ouantitv of the separated gas relative to time; andrecording said measurements relative to the well borehole depth.

6. A method of logging a well borehole comprising: passing a variablecurrent between a pair of spaced electrodes vertically shiftable withinsaid borehole and in electrical contact with aqueous fluid thereinwhereby said current flows through said uid between said electrodes andhydrogen is generated in said liuid at at least one of said electrodesby electrolysis in quantities which are representative of the values ofsaid current; varying said current in response to and as a function ofthe values of a quantity to be measured within the borehole, circulatingsaid fluid containing said hydrogen to the top of the well borehole, andthere measuring the quantity of separated hydrogen in said uid.

7. A method for logging a well borehole comprising: passing a variableD.C. current between a pair of spaced electrodes vertically shiftablewithin said borehole and in electrical contact with aqueous uid thereinwhereby said current flows through said iluid between said electrodesand hydrogen is generated in said uid at one of said electrodes byelectrolysis in quantities which are representative of the values ofsaid current; varying said current in response to and as a function ofthe values of a quantity to be measured within the borehole, circulatingsaid uid containing said hydrogen to the top of the well borehole, andthere measuring the quantity of the hydrogen in said iuid; andcorrelating the resultant measurements with the well borehole depth.

8. A method of logging a well borehole comprising: passing a variablecurrent between a pair of spaced electrodes vertically shiftable Withinsaid borehole and in electrical contact with aqueous tluid thereinwhereby said ured; circulating said fluid containing said hydrogen tothe top of the well borehole, and there measuring the quantity of thethus separated hydrogen relative to time; and correlating the resultantmeasurements with the well borehole depth.

References Cited in the le of this patent UNITED STATES PATENTS1,819,923 Schlumberger Aug. 18, 1931 2,238,903 Lieneweg Apr. 22, 19412,296,030 Hall Sept. 15, 1942 2,341,169 Wilson et al. Feb. 8, 19442,380,520 Hassler July 31, 1945 2,388,141 Harrington Oct. 30, 1945

